1. Field of the Invention
The present invention relates to a single crystal producing method and apparatus, and more specifically, it relates to a production method and apparatus of a single crystal for use in optics such as optical isolators or electronic components such as microwave isolators by the light-condensing and heating method.
2. Description of the Related Art
Materials for an optical isolator include an iron garnet (for example, Y3Fe5O12; hereinafter referred to as xe2x80x9cYIGxe2x80x9d) single crystal having a large angle of Faraday rotation. Recently, the demand for small-sized and sophisticated electronic components has increased. While a polycrystal such as ceramic sufficiently worked well in the past, a single crystal having no effect of grain boundary has been required along with demands on a size reduction. A YIG single crystal is also increasingly required.
Typical methods of growing a single crystal including the CZ (Czochralski) method are well known. Of these methods, the light-condensing and heating method representative of the FZ (Floating Zone) method is advantageous in that a high purity can be maintained because the crystal need not be in contact with crucible materials, in that the growth rate can be high because a large temperature gradient can be attained, etc.
A single crystal growth method using a combination of the light-condensing and heating method and the laser heating method, which is known as the LHPG (Laser Heat Pedestal Growth) method, is published in, for example, Japanese Unexamined Patent Application Publication No. 6-048883. A single crystal producing apparatus using this method is published in Japanese Unexamined Patent Application Publication No. 7-315979. Advantageously, this method employs a laser beam as a primary heat source to provide the temperature gradient more sharply, resulting in a higher growth rate. The present inventors disclose in Japanese Unexamined Patent Application Publication No. 10-251088 a single crystal producing method (SSFZ method) which takes advantage of a self-adjusting reaction.
This method is innovative in that an incongruent melting type of single crystal can be grown while being controlled in orientation.
When a laser beam is used to melt a polycrystal raw material rod, a YAG laser is commonly used. This is because a YAG laser can easily attain a light beam having a high output as well as a high linearity. A YAG laser beam having a high output and a high linearity can be used as a heat source without any condensing instrument such as lens.
A YAG laser beam has a wavelength of 1,060 nm and thus has drawbacks with respect to low light absorption of iron garnet. Therefore, a higher laser output is required, causing a deterioration of energy efficiency to thereby increase the operating cost. Furthermore, a YAG laser device is relatively expensive, increasing the investment for equipment. For these reasons, the single crystal production becomes costly, and it is therefore difficult to offer an inexpensive single crystal.
Accordingly, the primary object of the present invention is to provide a less expensive single crystal by attaining an increased growth rate of a single crystal, and an increased production, and by lowering the investment for equipment per unit cost.
The single crystal producing method for growing a single crystal comprises the steps of: placing a material at one focal point in a light-condensing and heating furnace having an ellipse in section; placing a heat light source at another focal point;
and emitting a laser beam has a wavelength of not less than about 160 nm and not greater than about 1,000 nm, on or near the one focal point to form a melt zone; and moving the melt zone to grow a single crystal. The wavelength of the laser beam preferably has a not less than about 750 nm and not greater than about 1,000 nm, and the single crystal is preferably magnetic garnet.
According to the another aspect of the present invention, the single crystal producing apparatus for growing a single crystal comprises: a light-condensing and heating furnace having an ellipse in section and first and second focal points on which light is condensed, the light-condensing and heating furnace holding a material stick at the first focal point; a heat light source provided at the second focal point; a laser emitting a laser beam on or near the first focal point to form a melt zone in the material stick, the laser beam having a wavelength within the range of about 160 to about 1000 nm; and a drive system to move the material stick with respect to the laser beam so as to move the melt zone in the material stick.
According to the present invention, since a laser beam having a shorter wavelength and having a higher light absorption than those of a conventional YAG laser beam, an efficient growth of single crystal can be achieved, making it possible to produce a single crystal at lower costs.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.